OBJECTIVETo study whether the live attenuated AroA-auxotrophic mutant of Salmonella (S.) typhimurium (SL7207) could be used as DNA delivery vehicle to induce more efficient immune response by using the eukaryotic expression plasmid pCMV-beta as report gene.

METHODSMurine peritoneal macrophages were infected with SL7207(pCMV-beta) in vitro, then the expression of the beta-gal were detected by X-gal staining or RT-PCR. After mice were orally immunized with SL7207(pCMV-beta), the expression of beta-gal in the lymphoid tissue were tested by RT-PCR, humoral responses were tested by ELISA, splenic lymphocyte proliferation were tested by 3H-TdR incorporation and cytotoxic T lymphocyte reaction were tested by JAM test.

RESULTSThe results indicated that the plasmid pCMV-beta could be delivered by SL7207 into the nucleus of the murine macrophages efficiently and expressed well in vitro; after mice received oral immunizations with attenuated S.typhimurium SL7207 harboring plasmid pCMV-beta mice, the expression of beta-gal could be detected in the spleen, mesenteric lymph nodes and Peyers patches of the mice. Furthermore, the experiments demonstrated that specific humoral immune responses and cell-mediated immune responses were successfully induced in these immunized mice. Compared with the naked DNA vaccination, SL7207 (pCMV-beta) oral immunization were more efficient in inducing cellular immune responses.

CONCLUSIONSAttenuated Salmonella typhimurium SL7207 could be used as DNA delivery vehicle for oral immunization, which have the ability to deliver the antigen-encoding DNA specifically to APC directly for inducing the specific immune response being dominant with cellular immune response.